Due to the high level of crystallinity of PPS, monofilaments thereof tend to be brittle and are difficult to work with. In particular, the knot strength, loop strength and fatigue resistance of PPS monofilament are all low and result in problems during the processing of the monofilaments, especially when the monofilament is woven into fabrics. When the monofilament is removed from the quill during weaving, twists and loops form which, when tightened, kink and result in filament breaks.
The production of fibers from aromatic sulfide polymers such as PPS is discussed in U.S. Pat. No. 3,895,091 which requires a partial cure of the polymer prior to melt spinning, followed by the extrusion and drawing. High modulus, high melting, non-burning polyphenylene sulfide fibers having good corrosion resistance properties are obtained as a result.
Mixtures of PPS with various thermoplastic materials have been prepared heretofore, in an effort to improve physical properties. In general, the mixtures are not directly extrudable or have not provided the improvement desired or both.
In U.S. Pat. No. 4,421,588, PPS is blended with polyetheretherketone using diphenylsulphone as a mutual solvent. The resulting mixture, used for bearing material, has high fatigue strength and improved thermal stability but can be formed only by molding.
In U.S. Pat. No. 4,455,410, PPS is mixed with a polyetherimide for the purpose of obtaining a material with good flexural strength and better mechanical properties than PPS alone. The PPS used in the example was Ryton P-4, a molding grade resin, available from Phillips Chemical Co. and which is suitable for molding rather than extruding. The final products described in the patent were produced by extruding a mixture of the components and then molding the mixtures, i.e., a two step process.
In U.S. Pat. No. 4,493,917, PPS (Ryton P-4, molding grade material) is mixed with fluoropolymers in order to improve the properties of the fluoropolymer which in turn is reflected in a modification of the mechanical properties of the components of electrochemical reactors that are made from fluoropolymers, viz., to reduce the high temperature creep and reduce the high thermal coefficient of expansion of the fluoropolymers. The fluoropolymers specified were fully fluorinated homopolymers or perfluoroalkoxy resins. The process of preparing the components required two steps: preparing the blend by extrusion and then producing the final object by molding.
U.S. Pat. No. 4,610,916, recently issued to the Assignee of record, discloses blends of polyphenylene sulfide with copolymers comprising olefins and halogenated monomers as well as a process for reducing brittleness in polyphenylene sulfide monofilaments.
It is also known to combine polyphenylene sulfide with various polymers for other purposes. U.S. Pat. No. 4,025,582, for instance, discloses the use of polyphenylsulfide as a ultraviolet stabilizer for polyolefin blends. The olefins are those having from 2 to 8 carbon atoms. The amount of polyphenylene sulfide is disclosed at 1 to 10 weight percent and its particle size distribution is such that it passes through a sieve of 100 to 200 mesh (U.S. Sieve).
U.S. Pat. No. 4,454,189 discloses fibrous sheets of copolymerized polyphenylene sulfide filaments with a thermosetting resin and a process for producing the same. The sheet is formed by conveying electrostatically charged extrudated polyphenylene sulfide filaments from small holes by a high velocity air stream. Interlocking is accomplished by needle punching or use of a water jet. The resultant sheets are useful as industrial filters, heat insulating materials, and electrical insulating materials.
U.S. Pat. No. 4,544,700 discloses a polyarylene sulfide composition containing polyphenylene sulfide, a low density ethylene polymer, and a reinforcing material such as glass or carbon fibers. The amount of polyphenylene sulfide is disclosed at 50 to 65 weight percent. The composition is injection molded by extrusion at an elevated temperature. The resultant compositions are useful as molding compositions for thick walled articles.
Thus, it will be seen that the present invention has provided improved properties for polyphenylene sulfidecontaining monofilaments by the addition of various polymers to form blends. Among these properties are better fatigue resistance and increased tenacity without sacrifice of chemical resistance or significantly lowering the use temperature. Also the extrudability of this monofilament has been improved by the process of the invention. Moreover, with the exception of U.S. Pat. No. 4,610,916, extrudability has not been satisfactorily addressed by the art discussed herein.